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don't use env with infer vars #151871

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Merged
rust-bors merged 2 commits into from
Feb 22, 2026
Merged

don't use env with infer vars #151871

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c316bdf
don't use env with infer vars
lcnr Jan 29, 2026
642d9c4
modernize comments about typing modes
jdonszelmann Feb 19, 2026
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20 changes: 13 additions & 7 deletions compiler/rustc_trait_selection/src/traits/coherence.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -498,22 +498,19 @@ fn impl_intersection_has_negative_obligation(
) -> bool {
debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);

// N.B. We need to unify impl headers *with* intercrate mode, even if proving negative predicates
// do not need intercrate mode enabled.
// N.B. We need to unify impl headers *with* `TypingMode::Coherence`,
// even if proving negative predicates doesn't need `TypingMode::Coherence`.
let ref infcx = tcx.infer_ctxt().with_next_trait_solver(true).build(TypingMode::Coherence);
let root_universe = infcx.universe();
assert_eq!(root_universe, ty::UniverseIndex::ROOT);

let impl1_header = fresh_impl_header(infcx, impl1_def_id, is_of_trait);
let param_env =
ty::EarlyBinder::bind(tcx.param_env(impl1_def_id)).instantiate(tcx, impl1_header.impl_args);

let impl2_header = fresh_impl_header(infcx, impl2_def_id, is_of_trait);

// Equate the headers to find their intersection (the general type, with infer vars,
// that may apply both impls).
let Some(equate_obligations) =
equate_impl_headers(infcx, param_env, &impl1_header, &impl2_header)
equate_impl_headers(infcx, ty::ParamEnv::empty(), &impl1_header, &impl2_header)
else {
return false;
};
Expand All @@ -531,7 +528,16 @@ fn impl_intersection_has_negative_obligation(
root_universe,
(impl1_header.impl_args, impl2_header.impl_args),
);
let param_env = infcx.resolve_vars_if_possible(param_env);

// Right above we plug inference variables with placeholders,
// this gets us new impl1_header_args with the inference variables actually resolved
// to those placeholders.
let impl1_header_args = infcx.resolve_vars_if_possible(impl1_header.impl_args);
// So there are no infer variables left now, except regions which aren't resolved by `resolve_vars_if_possible`.
assert!(!impl1_header_args.has_non_region_infer());

let param_env =
ty::EarlyBinder::bind(tcx.param_env(impl1_def_id)).instantiate(tcx, impl1_header_args);

util::elaborate(tcx, tcx.predicates_of(impl2_def_id).instantiate(tcx, impl2_header.impl_args))
.elaborate_sized()
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